1. INTRODUCTION
The increasing need for petroleum is a challenge that needs to be anticipated by finding alternative energy sources. Petroleum is a non-renewable energy source, it takes millions or even hundreds of millions of years to convert petroleum raw materials into petroleum, the increase in the amount of petroleum consumption causes the depletion of petroleum. Of the various petroleum processed products used as fuel, the most widely used is diesel fuel, because most transportation equipment, agricultural equipment, heavy equipment and power generator drivers use this fuel.
Biodiesel is one solution to these problems. Biodiesel is an alternative fuel to replace diesel oil produced from vegetable oil or animal fat. The use of biodiesel can be mixed with petroleum diesel (solar) [1]. Biodiesel is easy to use, biodegradable, non-toxic, and free from sulfur and aromatic compounds. In addition, biodiesel has a higher flash point than petroleum diesel so it is safer to store and use.
The use of palm oil or other vegetable oils as diesel fuel causes a problem because of the high viscosity which can cause damage to the engine. To overcome this, the oil can be reacted with short-chain alcohol with the help of a catalyst, this process is known as transesterification or alcoholysis. Transesterification with a base catalyst usually uses alkali metal alkoxides, NaOH, KOH, and NaHCO3 as catalysts. This base catalyst is more effective than an acid catalyst, the conversion of the results obtained is greater, the time required is also shorter and can be done at room temperature [2]. The metal from the base is extracted into the alcohol which then reacts with the alcohol to form a nucleophilic alkoxide, the alkoxide will attack the carbonyl group. This reaction is followed by an elimination stage which produces new esters and alcohols. In general, the transesterification reaction of oil with alcohol can be written in Figure 1.
The use of this catalyst can be replaced by using empty oil palm bunch ash (ATKKS), the result of burning empty oil palm bunches in the form of ash turns out to have a fairly high potassium content of 30-40% as K2O. Bunch ash turns out to have a composition of 30-40% K2O, 7% P2O5, 9% CaO, 3% MgO and other metal elements [3]. By dissolving a certain amount of ATKKS into a certain amount of alcohol (methanol or ethanol), potassium metal will be extracted into the alcohol and is expected to react further to form methoxide salt if using methanol or ethoxide salt if using ethanol. This salt will help accelerate the transesterification process of vegetable oil.
It is known that palm oil processing in addition to producing CPO (Crude Palm Oil) also produces by-products and waste, which if not treated properly will have a negative impact on the environment. One ton of fresh oil palm fruit bunches contains 230-250 kg of empty oil palm bunches (TKKS), 130-150 kg of fiber, 65-65 kg of shells and 55-60 kg of seeds and 160-200 kg of crude oil [3]. The use of empty oil palm bunches has so far been as a substrate in mushroom cultivation, boiler fuel, and burned to utilize the ash.
The manufacture of biodiesel from palm oil with empty fruit bunch ash catalyst is expected to be able to overcome various problems, including increasing the selling value of palm oil when palm oil products are flooded in the market, adding to the treasury of alternative fuel research, and optimizing the use of palm oil not only as oil products but also waste produced by the industry.
The use of ATKKS for the biodiesel manufacturing process has also been carried out by the previous author team [4,5]. Yoeswono first used ATKKS as a base catalyst in the transesterification of coconut oil [4], then Yoeswono also used ATKKS as a base catalyst to convert palm kernel oil into biodiesel [5]. Oil palm trees basically produce two types of oil, namely palm kernel oil and palm fruit oil (Crude Palm Oil, CPO). Palm kernel oil is mostly used as a raw material for margarine, while CPO is currently widely used as a raw material for cooking oil. From an economic perspective, the price of CPO is cheaper so it is more potential if processed for the purpose of being a raw material for biodiesel. For that, the research team used palm oil obtained from this CPO. Thus, this study will complement the knowledge about the potential of ATKKS as a base catalyst for transesterification.
RESEARCH METHOD
Materials
Palm oil, ATKKS obtained from palm oil mill boiler waste in the South Sumatra region. The chemicals used consist of technical methanol from Brataco Chemika, anhydrous Na2SO4 p.a (Merck), and distilled water.
Tools
The equipment for making biodiesel consists of a set of glassware, a set of reflux apparatus (three-neck flask with a capacity of 500 mL, thermometer, magnetic stirrer, electric heater, cooling system), stopwatch, electric scales, a set of distillation apparatus (500 mL distillation flask, electric heater, cooling system), 100 mesh filter, mortar and porcelain cup, oven, GC-MS (Shimadzu QP-5000), Atomic Absorption Spectrophotometer (AAS). Equipment for biodiesel quality analysis consists of ASTM D 1298, ASTM D
97, ASTM D 2500, ASTM D 93, ASTM D 445, and ASTM D 482 (Production Testing Laboratory of Oil and Gas Education and Training Center)
Working Procedure
Preparation of Empty Palm Oil Bunch Ash
The EFB is ground with a mortar and filtered with a 100 mesh filter. Furthermore, the ash is dried in an oven at a temperature of 110°C for 2 hours. Characterization of EFB ash is carried out by AAS test and indicator titration.
Biodiesel Making Process
A certain amount of EFB is soaked in 75 mL of methanol (BM = 32.04 g mol-1) for ± 48 hours at room temperature. The extract obtained was made up to a certain volume so that a certain methanol/oil mole ratio was obtained which would be used to transesterify 250 g of bulk cooking oil (assuming that the bulk cooking oil is palm oil with BM = 704 g mol-1).
Transesterification was carried out in a three-necked flask with a capacity of 500 mL, equipped with an electric heater, thermometer, magnetic stirrer, and cooling system, reflux was carried out at room temperature. 250 g of bulk cooking oil was weighed and poured into a three-necked flask, then assembled with a cooling system. A certain amount of the prepared methanol solution was poured into the three-necked flask, and the magnetic stirrer was turned on. The reaction time was recorded from the time the magnetic stirrer was turned on.
After the reaction had been running for 2 hours, the stirring was stopped, the mixture formed was poured into a separating funnel, and the separation was allowed for 2 hours at room temperature. The methyl ester layer formed was separated from the glycerol layer, then distilled to a temperature of 74 °C to remove residual methanol. To remove the remaining catalyst and glycerol in the methyl ester, washing was carried out using distilled water repeatedly, until a clear water layer was obtained.
Although the presence of water is unavoidable, it turns out that at mole ratios of 9:1 and 12:1 no soap solids are formed. The use of excessive methanol further slows down the rate of hydrolysis (saponification) of esters because methanol in the form of methoxide ions reacts quickly with triglycerides to produce methyl esters. However, at mole ratios of 9:1 and 12:1, a kind of emulsion is formed that is rather difficult to separate in the methyl ester mixture. This is because excessive methanol dissolves glycerol, the concentration of which is increasing. The emulsion formed at a mole ratio of 12:1 is more difficult to separate than at a mole ratio of 9:1. Thus, the addition of the methanol-oil mole ratio tends to cause an emulsion in the methyl ester mixture while making it difficult to recover glycerol dissolved in methanol. The emulsion will disappear with standing for some time (2-3 days) and through filtration.
The decrease in conversion at a ratio of 12:1 is also likely caused by excessive methanol dissolving in the glycerol formed. As a result, methanol that reacts with triglycerides to form methyl esters is reduced. In addition, with the increase in ester and glycerol yields that continue to form during the reaction, the reaction can reverse direction to form intermediate compounds such as monoglycerides. This as stated by Krisnangkura and Simamaharrnnop in Encinar et al. that the presence of glycerol can cause the equilibrium to shift back to the left (reactant) thereby reducing the ester yield [1]. The increase in methyl ester conversion with the addition of methanol moles is also related to the distribution of the catalyst between the ester layer and the glycerol layer. In the transesterification of palm oil with a mole ratio of 3:1, it is possible that the catalyst is more attracted to the glycerol layer and this according to the literature that for a molar ratio of methanol/oil of 3:1, the catalyst is more attracted to the glycerin layer [1]. Therefore, the catalyst is not sufficiently available in the ester layer, which causes the transesterification to not run perfectly. In other words, not all triglycerides react to form methyl esters. Furthermore, according to Junek and Mittel, excessive methanol causes the catalyst distribution to be more even in both the ester and glycerol layers. Based on this statement, this experiment shows that the use of excess methanol which causes the catalyst distribution to be more even in the ester and glycerol layers is followed by an increase in the conversion of methyl esters to the optimum limit at a methanol-oil mole ratio of 9:1.
Analysis using GC-MS aims to determine the components contained in biodiesel and to determine the quantity of each component. The percentage of biodiesel components resulting from conversion of palm oil is presented in Table 3.
In Table 3 it can be seen that methyl palmitate is the main component of biodiesel with the largest percentage, because palmitic acid in palm triglycerides (oil) is the largest component. In the conversion of biodiesel from a ratio of 9:1, methyl palmitate was obtained at 46.79%, then followed by methyl laurate as the second largest component at 18.25% and the rest is methyl esters derived from other fatty acids that make up palm oil, namely
Complete biodiesel product characteristic data is presented in Table 4. Biodiesel characteristics were tested using standard test equipment ASTM D 1298 for specific gravity, ASTM D 97 for pour point, ASTM D 2500 for cloud point, ASTM D 93 for flash point, ASTM D 445 for kinematic viscosity, and ASTM D 482 for ash content.
To determine the quality of the biodiesel produced, it can be seen from the biodiesel characteristic test data as listed in Table 4. The addition of methanol moles in the transesterification of palm oil is accompanied by a decrease in viscosity, from a pure oil viscosity of around 30 cSt to 3.063 cSt for biodiesel with a reactant ratio of 9:1. The addition of methanol moles causes the biodiesel produced to be purer because more triglycerides are converted into methyl esters. The methyl ester mixture may still contain unreacted triglycerides, residual oil or long-chain hydrocarbon compounds. Of the four variations, only biodiesel with a reactant mole ratio of 3:1 with a viscosity that is not within specifications because it still exceeds the maximum allowable limit, and biodiesel with a mole ratio of 6:1 is slightly above the specified viscosity value.
Pour point is closely related to viscosity because the lower the viscosity, the easier it is for biodiesel to flow under certain conditions. The pour point values of all biodiesels are within specifications because they are still below 65 °F. The pour point values of 9:1 and 12:1 biodiesel are the same because both have almost the same viscosity. Another physical characteristic of biodiesel observed is the specific gravity at 60/60 °F. The specific gravity of biodiesel increases from a mole ratio of 3:1 to 6:1 and then decreases to a mole ratio of 12:1. The flash point characteristics of biodiesel are all within the specifications of standard diesel fuel with an average value above 65.5 °F. This character affects the safety of the fuel to be stored at certain temperature conditions. The higher the flash point value, the safer the fuel is to be stored at relatively low temperature conditions. The flash point of the biodiesel produced is quite good, namely above 100 °C.
Biodiesel has a low carbon residue character, so it can be said that the combustion of biodiesel is quite perfect without leaving much residue in the form of charcoal/carbon that can interfere with the operation of the diesel engine.
Unlike the physical characteristics of other biodiesels, the ash content of the biodiesel produced does not meet the specifications of standard diesel fuel. The high ash content in this biodiesel can be caused by the presence of impurities that have been contained in palm oil from the start. High ash content can interfere with the operation of the diesel engine.
CONCLUSION
Based on the results of the analysis of metals with AAS in ATKKS, potassium metal is the largest component (29.8% by mass). Potassium metal in ATKKS is possible in the form of carbonate compounds. This is proven by the alkalinity test on ATKKS. With the basic properties of potassium carbonate, ATKKS has the potential to be used as a source of base catalysts in the manufacture of biodiesel. The addition of the mole ratio of methanol to oil increases the conversion of biodiesel and reaches the maximum conversion condition at a mole ratio of 9:1 of 84.12%. The physical characteristics of the resulting biodiesel product generally meet the criteria for standard diesel fuel specifications.